Silphium pinnatifidum - Cutleaf Rosinweed, Cutleaf Prairie Dock, Tansy Rosinweed, Southern Dock. Rosinweeds look very similar to sunflowers, but the seeds form from the ray flowers in rosinweeds, and from the disk flowers in sunflowers. Silphium pinnatifidum can be to 10' tall, and has numerous heads on branching, nearly leafless stems. S. pinnatifidum is considered by some botanists to be a variety of S. terebinthinaceum, with the primary difference being the deeply lobed (almost to the central vein) leaves in S. pinnatifidum. The basal floret of leaves in S. terebinthinaceum are spade-like.